The recursive mathematical model of the porous media is developed, in which the structure of a porous macroparticle is represented as a system of finer porous particles (microparticles), each of which in turn also consists of a next level system of porous microparticles, etc. The porous structure of microparticles of each level is described by a model of chaotically located spheres. This recursive model is used for developing a mathematical model of chemical reaction in the porous media describing speeds of reagent supply to a reactionary surface as a function of internal structure of a particle, diffusion resistance of microparticles of various levels being accounted. Calculations of a high-temperature pyrolysis process of methane in the porous carbonized samples of wood are carried out. Satisfactory agreement with experimental data is received. (c) 2006 Elsevier Ltd. All rights reserved.